Method for controlling the profile of workpieces on rolling mills

ABSTRACT

There is described a method for controlling the profile of a workpiece on a rolling mill, wherein the workpiece is imparted with a predetermined profile in the roughing stage which is suitable for further control in the following finishing stage. In the finishing stage, the desired profile of the workpiece is attained by adjustment of one or a combination of factors including modifying the rolling loads of the respective roller stands preceding the last stand, cooling of the rolls, and changing the rolling pitch. The final shape control of the workpiece is carried out on the last stand. The adjustment of the rolling load is performed by simulating the desired workpiece profile by means of an even ordered function whose constants represent the load determining factors and by adjusting such constants in accordance with the desired changes in the load conditions.

United States Patent 1191 Kawamoto et a1.

[ 1 May 13, 1975 METHOD FOR CONTROLLING THE PROFILE OF WORKPIECES ONROLLING MILLS [75] Inventors: Toshiharu Kawamoto; Yoji Itoh;

Kouji Hiyoudo, all of Sakai; Kenya Fukushima, Himeji, all of Japan [73]Assignee: Nippon Steel Corporation, Tokyo,

Japan [22] Filed: Oct. 15, 1973 [21] Appl. No.: 406,352

[30] Foreign Application Priority Data Oct 16, 1972 Japan 47-10277] [52]US Cl. 72/234; 72/6; 72/16; 72/366 [51] Int. Cl B21b 1/22; B21b 37/00[58] Field of Search 72/6, 8-12,

3/1971 Fischer et a1, 72/8 11/1971 Sabatini et a1. 72/8 OTHERPUBLICATIONS Primary E.wminerMi1ton S. Mehr [57] ABSTRACT There isdescribed a method for controlling the profile of a workpiece on arolling mill, wherein the workpiece is imparted with a predeterminedprofile in the roughing stage which is suitable for further control inthe following finishing stage. In the finishing stage. the desiredprofile of the workpiece is attained by adjustment of one or acombination of factors including modifying the rolling loads of therespective roller stands preceding the last stand, cooling of the rolls,and changing the rolling pitch. The final shape control of the workpieceis carried out on the last stand. The adjustment of the rolling load isperformed by simulating the desired workpiece profile by means of aneven ordered function whose constants represent the load determiningfactors and by adjusting such constants in accordance with the desiredchanges in the load con- 10 Claims, 11 Drawing Figures [56] ReferencesCited UNITED STATES PATENTS 3,049,950 8/1962 Pearson r r I. 72/83,248,916 5/1966 Kenyon et a1 72/16 X diti ng,

3,387,470 6/1968 Smith 72/7 3,475,935 11/1969 Kajiwara 72/9 1 4 m2 Fl F56 F6 f TENTH] HAY I 3W5 SHEET 1 BY FIG.

FIG.3

FIG.2

mum

FCRmin FCRmax FCR TARGET A JV AVAVA 7 (2) F6 PROFILE CONTROL STOP T A vEX.2 EX.3

SHAPE CONTROL START g mmiomm (I) LONGITUDINAL STRETCH AT EDGES (2)LONGITUDINAL STRETCH AT CENTER FIG.4

PATENTEB HA! I 3 I975 SHEET 2 BF 3 FIG.6

PLATE WIDTH, ROLLING FORCE FIG.7

FIG

[I'll-Ill 3 ITI h- PZQQWEMOQ @ZFOMKEOU Wu PLATE WIDTH M STRETCH FIG.|O

FIG.9

F ROLLING FORCE I [CALCULATING RP, RCI

PIIIENIED HAY I 3 BIS SHEET 3 BF :3

FIG.II

CALCULATING CV CALCULATING Wv| IgXPONENTIALLY SMOOTHING CI,b

I LESTIMATING Cv,Wv OF NEXT COIL] DNHETHER ESTIMATED Cv EXCEEDING LS ZIYES CALCULATING LD [WHETHER LD EXCEEDING LS AL YES CRAMPING LDCALCULATING RP, RC I CALCULATING IRC ICALCULTATING ROUGH Cv BY RLD ORRB] I [WHETHER RLD EXCEEDING LS l YES CRAMPING RLD [RE 'CALCULATINGFINISH LD1 CALCULATING? IRC TAKING REFFERENCE LD OF THIS JBAR TAKINGTHIS B I TAKING FINISH LM OF. THIS BAR I ROUGH LM OF AR Rsg METHOD FORCONTROLLING THE PROFILE OF WORKPIECES ON ROLLING MILLS FIELD OF THEINVENTION The instant invention relates to a method for controlling theprofile of a plate being rolled on a rolling mill to a desired shape.

BACKGROUND OF THE INVENTION As is well known in the art, a rolled plateactually contains, variations in its thickness both in the transverseand the longitudinal directions. The variations in the transversedirection which is across the width of the plate, is expressed in termsof the crown and the wedge which together define the profile of theplate. The Crown is the difference between the thickness along thelongitudinal centerline of the plate and the thickness at thelongitudinal side edges of the platev The Wedge is the difference inthickness between the front and rear ends of the plate (lzw 12d).

In order to adjust the profile of a plate workpiece, it has been thegeneral practice to measure the thickness of the plate at variouspositions across its width to enable an operator to make appropriateadjustments such as in the rolling pitch, rolling load distribution,reduction on the driving side as well as on the working side of themill, and thus to modify the profile based on the actual measuredvalues. However, this method presents inconveniences in that themeasurement takes a relatively long time and a modification of therolling load imposes adverse effects on the plate temperature andprecision of the plate thickness. Furthermore, adjustment of the rollingpitch leads to reductions in working efficiency, and adjustment byreduction of the driving side or the working side often entails problemsrelating to proper passage of the plate through the rolls. Obvi ously,taking into consideration the aforementioned problems, the determinationof the optimum values of each of the corresponding factors isprohibitively complicated.

SUMMARY OF THE INVENTION Based on theoretical and experimental studieson the profile control of a plate undergoing hot rolling, the presentinvention contemplates solving the problem of how to distribute thecorrection in the crown and wedge values to a number of roll stands inthe roughing and finishing stages or mills. The present invention issupported by the findings in these studies and is directed to a methodwhich is capable of providing an optimum profile control.

In hot rolling using a number of roll stands, a limitation is naturallyimposed on the profile control capability of each stand. In order toroll a workpiece into a desired profile, a load corresponding to thedesired profile should be distributed among the respective roll stands.

In view of the practical problems of actual control mechanisms andadjustments of control settings, the workpiece is preferably rolled intwo stages or mills: the roughing mill and the finishing mill. Theworkpiece is imparted with a rough profile in the roughing stage to adegree suitable for facilitating final shaping into the desired profilein the following finishing stage. In other words, the roughly profiledworkpiece is finished into the desired profile with high precision inthe finishing stage of the rolling. It is preferable to employ aplurality of roll stands in the finishing stage. The rolling loadrequired to obtain the desired profile is then distributed to all of theroll stands in the finishing stage with the exception of the last onewhich performs only shape control. Instead of employing a largeplurality of roll stands, there may be employed a system using one orseveral reciprocating multi-roll stands, while distributing the rollingloads to each pass. The load distribution as mentioned above shouldpreferably be applied also to the roll stands in the roughing stage.

The profile control during rolling is performed on the basis of factorssuch as adjustment of the roll cooling temperature and adjustment of therolling pitch.

The rolling profile can be simulated in terms of an even orderedfunction whose constants correspond to the control factors in actualrolling. It is therefore possible to control the rolling profile byadjusting of the constants thereby effectively adjusting the controlfactors.

It is a primary object of the instant invention to provide a method forcontrolling the profile of a workpiece on a rolling mill to impartthereto a desired profile.

It is another object of the present invention to provide a method forcontrolling the profile of a workpiece on a rolling mill withoutimposing adverse effects on the shape of the workpiece as a result ofthe profile control.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description, taken inconjunction with the accompanying drawings which are employed for thepurpose of facilitating the understanding of the present invention andnot for the purpose of placing thereon any limitation whatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a cross-sectional view of a generally used workpiece;

FIG. 2 is a graphical representation of the relationship between thefinishing crown ratio (FCR) and the roughing crown ratio (RCR) as willbe obtained in accordance with the workpiece profile control method ofthe present invention;

FIG. 3 is a block diagram showing a portion of a rolling system employedin the present invention;

FIG. 4 is a graphical representation of profile errors (EX.1 and EX.2)occuring when utilizing a conventional method and profile errors (EX.3)occuring when utilizing present invention;

FIG. 5 is a graphical representation of the relationship between thebending force and crown variations of the roll stand in accordance withthe present invention;

FIG. 6 is a graphical representation of the relationship betweencorrection coefficients n 11 plate width (or workpiece width) androlling force of a roll stand when utilizing the present invention;

FIGS. 7 to 10 are graphical representations of characteristics of arolling system utilizing the present invention; and

FIG. 11 is a block diagram or a flow chart explaining a workpieceprofile control method embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows in a somewhatexaggerated manner the cross-section of a plate which has been rolled byan ordinary method. As shown, the rolled plate P has a varying thicknesswhich is largest in the middle of the plate, as indicated by lit", andis smaller at the side edges as indicated by hw and hd. The plate thushas a crown of he (hw hd)/2 and a wedge of hw lid. The causes of thecrown and wedge are well known and it has been the conventional practiceto. control them to within predetermined values using a finishing stand.However, such control of the crown often results in wavy edges along theplate as well as overstretching in the middle of the plate which impairsthe shape namely the flatness of the plate. In order to avoid suchimpairment of the shape, it is necessary to bring the profile into anallowable range by rough correction as early as in the roughing stage ofthe rolling.

This relationship is shown graphically in FIG. 2 where the ordinaterepresents the rough crown ratio (RCR) and the abscisa represents thefinish crown ratio (FCR). The crown ratio (RCR) or (FCR) is expressedRCR or FCR /2 (hd hw)/hc) The straight line 1 is a plot of RCR FCR andthe hatched area shows the allowable range of the crown ratio at the endof the finishing stage. A plate having a crown ratio within this rangeallows finish rolling without causing deterioration in its shape.

In the roughing stage the crown of the plate workpiece is thus correctedto have a value within the allowable range. Fine adjustments are thencarried out during the finishing stage so that the plate is impartedwith the final desired profile. However, if the last stand in thefinishing stage also performs crown control, there still results theadverse effects on the shape of the workpiece as mentioned hereinbefore.Therefore, in

the present invention, the workpiece undergoes no crown control from thelast stand of the finishing stage and the crown control is performed bya roll stand or stands preceding the last stand, preferably, by thefifth stand or, if necessary, by the fifth and other preceding standswhen the finishing stage includes six stands, the last stand performingonly the shape control. The same in connection with the Wedge control.By carrying out the crown and wedge control in this manner, it becomespossible to obtain a product with a desired profile and with excellentflatness.

FIG. 3 diagrammatically shows an arrangement of a mill carrying out theabove-mentioned control under various conditions, while FIG. 4 shows theresults of experiments conducted using the mill. In FIG. 3,. Fl to F6are the first to sixth stands of a tandem finish rolling mill. Alsoshown is a profile measuring device 1, a shape measuring device 2, aprofile control device 3, and a shape control device 4. Both profilecontrol and shape control were carried out by way of roll bending andreduction adjustments, and the rolling was carried out in the followingthree different ways.

EXAMPLE 1 Profile control only using all the tandem finish roll standsFl to F6.

EXAMPLE 2 profile control by using all the tandem roll stands Fll to F6and shape control by using stand F6.

EXAMPLE 3 Profile control by using the tandem finish roll stands I F1 toF5 and shape control only by the last roll'stand F6. This last examplebeing according. tothis invention. .5 g As is clear from FIG. 4, thecontrol in Example I atf tains a profile of the target value but showsanex-f tremely unsatisfactory flatness. The control in Example 2 alsoresults in a profile of the target value but is also I I incapable ofcorrecting the flatness even if the shape r control was utilized to itsmaximum. The control inExf 1 j ample 3, however issatisfactory both inprofile as well I as in flatness and a suitable flatnesscan be obtainedusing the capabilities of the shape control device. ,ltcan therefore beunderstood that the method ofthe inven i tion is greatly effective incontrolling the profile and r the shape of a plate being rolled; I

According to the present invention, the reduction adjustment isperformed in the following: mannenThe gree, as

wherein the coefficient a is determined bythe loaddis; I tribution forthe respective roll stands, the kind of} workpiece being rolled and theinitial roll curve. The coefficient b is determined by the deviationbetween i the roll center 0' and the plate center 0, and C is aconstant. For example, if the profile is expressed by thei quadraticequation of y a(x b) C of Equation (I), using the definitions mentionedabove, the crown C andthe wedge W can be expressed as follows (symbolsare as in FIG. 1):

the roll] b) +2c+2a( bywolij, I

From Equations (3) and (4), the contents of the quadratic equation y a(xb) C can be written as Actually by way of example the coefficients a, bare used by, exponentially smoothing the values obtained from theactually measured values C and W,..

On the other hand, in order to control a plate into a desired profile,since the wedge W,. is normally preferred to be zero b should be equalto zero. Thus, the coefficient a should be determined in accordance witha desired crown (1.. There are many factors which influence thecoefficient a and they are considered in the present invention asfollows.

wherein al represents the influence of the initial roll curve, a2represents the roll bending amount due to a rolling reaction force a3represents the resistance to deformation of the workpiece, and a4 is alearning term including heat crown and abrasive wear. For a desiredprofile the coefficient a can be calculated from the Equation (5) whilethe factors al, a3 and 04 can be accurately obtained by precalculationand as a result of learning. The roll bending amount a2 for the desiredprofile may be obtained from the following equation.

Once the roll bending amount a2 is obtained, the rolling reaction forceF,- required for producing such a roll bending amount can then beobtained as a function of a2, more particularly, as f (a2). The rollingreaction force F,- is introduced during the finishing process, on a rollstand positioned close to the final roll stand for imparting the desiredprofile to the workpiece. If the finishing stage includes six rollstands and the aforementioned rolling reaction force F is introduced,for example, by the fifth stand or other preceding stands, the referenceload distribution among the first six stands becomes unbalanced, causingirregularities in the total rolling amount. This, however, can becorrected by increasing or reducing the rolling load of the fourth andother preceding roll stands. If sufficient correction cannot be attainedwith such adjustment, it may be effected through rolling pitchadjustment and roll cooling adjustment.

The load distribution in the roughing stage can be effected in the samemanner as in the finishing stage. The crown desired to be producedduring the roughing stage, is determined from the relationship shown inFIG. 2. More particularly, the rough crown ratio is first obtained whichwill produce the allowable range of the finish crown ratio. Then, fromthe rough crown ratio RCR and the rough finish target thickness hHT, therough crown C is calculated as follows.

c,., hHT 1 RCR) The load distribution control is then effected in such amanner that the workpiece attains the desired rough crown ratio at theend of the roughing stage. However, the roll bender is also effectivefor controlling the crown ratio in the roughing stage. Since the bendingforce and variations in the crown resulting from such bending force,have the relationship as shown in FIG. 5, the difference between therough crown C in the preceding operation and the presently requiredrough crown C is obtained as A C,., C m C and the required referencebending force AT can be obtained from FIG. 5. The correctioncoefficients n, and 17 for the plate width and the rolling reactionforce are obtained from FIG. 6, from which the required bending force ATof the roll bender is calculated by the following equation.

AT}? 11 72) ATRS The crown correction effected through load distributionin the roughing stage is mainly performed by the last roughing rollstand with aid of one or two preceding stands which are adapted tocompensate for any deficient amounts in the correction. Afterdetermining the required rough crown C,., as discussed hereinabove, acorrection coefficient n for the plate width W1 is obtained from thegraph of FIG. 7 showing the relation between the plate W and the widthcorrection coefficient 1 required roll bending amount RCR, can becalculated from the equation.

Using the required roll bending amount RCR it is possible to obtain therequired reference rolling reaction force F from FIG. 9 and the requiredstretching rate A, from FIG. 8. The stretching rate A of the sixth andlast stand R6 in the roughing stage having six roll stands is expressedas A6 2 h, x, x hHT This is sequentially repeated to determine thethickness schedule in the roughing stage.

The rolling reaction force F,- is normalized based upon the kind, widthand temperature of the steel plate being rolled and converted into therequired rolling reaction force F, upon determination of the screw valuein consideration of the spring back of the rolling mill. That is,

This routine learning takes into consideration the learning of thecorrection coefficient 1 resulting from correction of the curve of FIG.8 and correction by the operator.

As already discussed with reference to FIG. 2, the allowable range ofthe finish crown ratio FCR is defined by the determination of the roughcrown ratio RCR. As a result, there are obtained a maximum adjustablecrown C and a minimum adjustable crown C,.,,,,-,, as follows.

AiM min) rmin AiM V nm.r)

( Next, al is inserted into Equation (3) with b O, to obtain the crownC, as follows.

where W0 represents the body length of the roll. The

value thus obtained is regarded as the initial roll curve but, inpractice, an initial roll curve K C, is employed using the correctioncoefficient K taking into consideration a particular schedule, or thelike.

The correction of the wedge can be effected through one or a number ofarbitrarily selected roll stands in the roughing stage. Forexample,where the stand R5 is used solely for this purpose, the correction iseffected by adjustment of the selsyn difference (levelling WS D5) of thefifth stand R5 and the last stand R6 is used for effecting a correctionsuch as of bending. The regressions measures of the extent to which twovariables increase together, or one increases while the other decreases)of the wedge amount W,., the levelling amount R'5 by the fifth stand R5,and the plate width Ware expressed as follows.

W,. 0.00866R5 0.00242W 0.94

Thus, in order to have a wedge of zero value, the levelling amount R'5of the stand R5 should be R'5 0.28W- 109 K (l/lOOm/i m) wherein K is alearning term.

FIG. 10 shows the relation between the wedge amount W, and the levellingamount R'5 of the fifth stand in accordance with Equation (17) using afixed plate width (W= W0). If the wedge amount W,. as obtained fromEquation (4) deviates from the reference value, levelling is effected inaccordance with Equation (18) and the term K is learnt in accordancewith a value measured by a profile meter.

If the levelling is effected in an amount R50 and the measured value ofthe wedge is W a levelling den:

ciency is obtained from FIG. was

The correcting amount is obtained by multiplying the. 5'

deficiency by the gain K That is,

KRNEW KROLI) KG m 6 i The aforementioned various means of profilecontrol are summarized in FIG. 11 by way ofa flow chart. In this figure,the symbol LS represents the limit of standard, LD the loaddistribution, RP the rolling pitch, RC 7. the roll cooling, IRC theinitial roll crown, RLD the roughing load distribution, RE the rollbender and LM the levelling mode.

It will be clear from the foregoing detailed descrip- I tionthat,according to the instant invention, the profile correction is suitablydistributed over the roughing and finishing stages and the correction oftheprofile is opti-i mally carried out by way of changing the loaddistribu-- tion and by means of the roll bender, so that the workpiececan be controlled with a desired profile to a high precision.

Since certain changes may be made in theabove described workpieceprofilecontrol method without de l T parting from the scope of theinventionasdefmed by i the appended claims, it is'intended that allmatter contained in the above description should be interpreted asillustrative and not in a limiting, sense. I We claim:

l. A method of controlling the crown of a workpiece passing through arolling mill comprising the steps of roughly adjusting the crown bymeans of a first roughing stage of the rolling mill to produce a profileon the workpiece which is within an allowable predetermined range for asuccessive second finishing stage of the rolling mill, and finelyadjusting the crown by means of said second, finishing stage oftherolling mill to pro' -w duce the desired profile on the workpiece byutilizing all but the final stand within said finishing stage.

2. The method of claim 1 further comprising the step; I of controllingthe flatness of said workpiece by adjusta ing said last stand.

3. The method of claim 1 wherein said crown is con-, trolled byadjusting the roll temperatures of the stands. 1 if 4. The method ofclaim 1 wherein the crown control I of said roughing stage is performedby adjusting, the roll.

benders.

ing of at least one roller of astand in said roughing stage. i

8. The method of claim 1 wherein saidcrown is corii trolled by modifyingthe load distribution among the stands.

9. The method of claim 8 wherein said modifyingoff the load distributionis effected by simulatingfthe de sired crown by an even ordered functionand altering;

the constants of said function to control the load distrifunction andaltering the constants of the function at bution among the stands. eachstands to control the load distribution among the 10. The method ofclaim 9 further comprising simustands.

lating desired crowns at each stands by an even ordered

1. A method of controlling the crown of a workpiece passing through arolling mill comprising the steps of roughly adjusting the crown bymeans of a first roughing stage of the rolling mill to produce a profileon the workpiece which is within an allowable predetermined range for asuccessive second finishing stage of the rolling mill, and finelyadjusting the crown by means of said second, finishing stage of therolling mill to produce the desired profile on the workpiece byutilizing all but the final stand within said finishing stage.
 2. Themethod of claim 1 further comprising the step of controlling theflatness of said workpiece by adjusting said last stand.
 3. The methodof claim 1 wherein said crown is controlled by adjusting the rolltemperatures of the stands.
 4. The method of claim 1 wherein the crowncontrol of said roughing stage is performed by adjusting the rollbenders.
 5. The method of claim 1 wherein said crown is controlled byadjusting the rolling pitches at the stands.
 6. The method of claim 1wherein wedge control of the workpiece is performed solely at saidroughing stage.
 7. The method of claim 6 wherein said wedge control ofthe workpiece is performed by modifying the leveling of at least oneroller of a stand in said roughing stage.
 8. The method of claim 1wherein said crown is controlled by modifying the load distributionamong the stands.
 9. The method of claim 8 wherein said modifying of theload distribution is effected by simulating the desired crown by an evenordered function and altering the constants of said function to controlthe load distribution among the stands.
 10. The method of claim 9further comprising simulating desired crowns at each stands by an evenordered function and altering the constants of the function at eachstands to control the load distribution among the stands.